This invention relates to a scroll compressor having a restriction in the back pressure chamber tap to provide more control over the operation of the back pressure chamber.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, opposed non-orbiting and orbiting scroll members face each other. Each of the scroll members have a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. The orbiting scroll is caused to orbit relative to the non-orbiting scroll, and compression chambers defined between the wraps are reduced in size to compress an entrapped refrigerant.
The scroll compressor combination generally includes one of the two members being able to move for a limited axial distance relative to the other. The compression of the refrigerant between the wraps presents a separating force tending to force the two scroll members away from each other. Historically, this separating force has been resisted by tapping a compressed refrigerant to a “back pressure chamber” defined behind the base of one of the two scroll members. The back pressure chamber creates a force forcing the base of the axially movable scroll member toward the other scroll member, thus resisting the separating force.
While the use of the back pressure chamber does address the separating force issue, there are certain challenges that remain. As one challenge, it may sometimes be desirable to not have the back pressure chamber operable for a period of time at start-up of the compressor. As an example, under certain conditions, it may be difficult to begin movement of the compressor members. In such a situation, it would be desirable to not have the back pressure chamber operable for a short period of time after start-up. In this way, the scroll members are not in contact with each other, and there will be leakage reducing the load on a motor for driving the orbiting scroll for a period of time.
Another challenge with back pressure chambers is that during operation, there is some fluctuation in the pressure at the point in the compression chambers from which the back pressure chamber refrigerant is tapped. These fluctuations cause fluctuations in the back pressure force, which may result in somewhat non-smooth operation. Furthermore, the fluctuations in pressure also result in high pressure refrigerant flowing from the compression chambers to the back pressure chamber. Since the back pressure chamber is at a lower pressure, this gas gets expanded, then later recompressed when the pressure tap moves to a lower pressure chamber. This recompression results in a power loss. Because the restrictor minimizes the flow of gas, it also minimizes the power loss due to recompression.